1. Field of the Invention
The present invention relates to a disc cartridge, and more particularly, to a disc cartridge having a case which accommodates a disc and centers the disc within an area in the case.
2. Description of the Related Art
FIG. 1 shows a conventional disc cartridge 1, which is loaded and unloaded in a slot-in manner, with a shutter 5 open. The disc cartridge 1 includes a case 3 which forms the outer appearance of the disc cartridge 1, and a circular inner wall 4 which encompasses a space where a disc D is placed therein. The circular inner wall 4 is spaced apart from an edge of the disc D by a predetermined gap ‘d’.
The case 3 includes an upper case 3a and a lower case 3b. A clamping area D3 of the disc D and an open portion 7 corresponding to a read/write area D4 of the disc D are located in the lower case 3b. The clamping area D3 and the open portion 7 are opened and shut by the shutter 5 guided by a shutter guide 6.
FIG. 2A shows a sectional view taken along line II-II′ of FIG. 1, in which the disc D is placed on a spindle hub 14. FIG. 2B shows an enlarged sectional view of an oval portion referenced by ‘a’ in FIG. 2A. Referring to FIGS. 2A and 2B, a disc clamp 8 which has a donut shape having a through hole at the center thereof is provided at the central portion of the disc D. A convex portion 9 where an inclined portion 9a is formed along an edge thereof is formed around the through hole at a bottom surface of the disc clamp 8. The disc clamp 8 is placed on the spindle hub 14.
The spindle hub 14 includes a guide portion 12 inclined corresponding to the convex portion 9 of the disc clamp 8 and a permanent magnet 13 which generates a clamping force with respect to the disc clamp 8. A spindle hub shaft 10 having a protruding portion 10a which centers the disc D with respect to the spindle hub 14, by entering the through hole of the disc clamp 8 of the disc D, is formed at the central portion of the spindle hub 14.
Loading and unloading operations of the disc cartridge 1 with respect to a slot-in type disc drive (not shown) are described in detail below with reference to FIGS. 1, 2A and 2B.
When the disc cartridge 1 is pushed into the slot-in type disc drive (“disc drive”), the shutter 5 is moved to one side along the shutter guide 6 to open the open portion 7 so as to allow an optical pickup (not shown) to access the read/write area D4 of the disc D. Here, the case 3 is firmly held by a loading/unloading apparatus (not shown) of the disc drive. When the inclined portion 9a of the disc clamp 8 is positioned within a corresponding inclined area of the guide portion 12, the disc D slides along an inclined surface of the guide portion 12 so as to have the disc clamp 8 and the spindle hub 14 engage with each other. Thus, the disc clamp 8 is accommodated on the spindle hub shaft 10 and firmly held by a magnetic force of the permanent magnet 13.
When the disc cartridge 1 is unloaded from the disc drive, the disc cartridge 1 is pressed in a direction indicated by an arrow A in FIG. 1 in which the disc cartridge 1 enters the disc drive. Here, only the case 3 is moved in the direction A in a state in which the disc D is firmly held on the spindle hub 14. Next, an unloading system (not shown) of the disc drive pushes the cartridge 1 in a direction opposite to the direction A of FIG. 1. Accordingly, a portion of the lower case 3b of the disc cartridge 1 adjacent to the disc clamp 8 is inserted between the disc clamp 8 and the spindle hub 14 to separate the disc clamp 8 from the guide portion 12. The separated disc cartridge 1 is unloaded from the disc drive and the shutter 5 is shut.
Thus, when the disc cartridge 1 having the above structure is unloaded, a gap in which the case 3 can move in a state in which the disc D is firmly held by the magnetic force of the spindle hub 14, is needed. That is, the gap ‘d’ between the outer circumference of the disc D and the circular inner wall 4 should be greater than a gap required for rotation of the disc D by a spindle motor (not shown). The disc D to be loaded moves within the above gap inside the case 3. When the disc D moved to one side in the disc cartridge 1 is to be accommodated on the spindle hub 14, since the inclined portion 9a of the disc clamp 8 must be designed to be positioned within an inclined area of the guide portion 12 corresponding to the inclined portion 9a, the width of the inclined portion 9a increases in proportion to the gap ‘d’ between the outer circumference of the disc D and the circular inner wall 4. Accordingly, the height of the convex portion 9 and the thickness of the disc cartridge 1 also increases, thereby preventing a miniaturization of the disc cartridge 1.